1. Technical Background
The present invention relates to a vascular filter with a sleeve covering, which can be temporarily or permanently placed inside a blood vessel for the purpose of intercepting thrombus.
2. Discussion
Some basic types of vascular filters are generally known, wherein a single filter element, mesh or member extends across the direction of flow inside a blood vessel. Several features may be desirable for vascular filters, including non-surgical or “percutaneous” delivery of the filter to a desired site, and expansion from a preferably small initial size to an expanded working size that matches the vascular anatomy at the desired site. Also, a vascular filter should preferably capture a sufficient percentage of thrombus, while allowing blood to flow freely through the filter.
Another desirable feature is a capability to remain reliably in the desired position in a patient's anatomy, referred to as “position retention.” One simple attempt at position retention is to wedge a vascular filter against the blood vessel wall by sizing it with a dimension slightly larger than the inside diameter of the blood vessel. In addition, a vascular filter should preferably have a design whereby the filter is self-centering and stable in the vessel, such that the filter has a tendency not to “tilt”, which might result in less effective capturing of thrombus. Some vascular filters may be used in the vena cava, and may be described in such event as a “vena cava filter.”
A vascular filter may be delivered through a catheter in a compressed shape, the filter tending to resiliently expand within a blood vessel and to retain the desired position and orientation. The vascular filter tends to trap thrombus or particles, and resist their movement further downstream. The filter includes, in a position of use, an outer shape corresponding to the internal diameter of the blood vessel, and one or more filter elements extending across the vessel.
In the temporal sense, there are three type of filters: (i) permanent filters, intended for permanent implantation; (ii) temporary filters, intended for removal within a time period; and (iii) retrievable filters, in which the physician has the option to implant the filter permanently or to remove the filter after some time. In the case of a retrievable filter, the filter may be designed so that the physician can choose whether to retrieve the filter at a later date, after the filter has been in place for a while. This way, the physician can evaluate the performance of the filter and the patient's condition, before deciding whether to retrieve the filter or not.
To help in successful retrieval, one factor is to avoid “endothelialization” or in-growth of the vessel wall and tissue around the structural members of the filter. In other words, endothelialization is the healing of the vessel inner surface by endothelial cells. It is desirable to preserve these endothelial cells when removing a retrievable vascular filter, and the improved designs of the present invention tend to minimize any impact during retrieval.
On a filter, it may also be desirable to provide releasable temporary position stabilizers, to resist tilting and to enhance position retention. Some vascular filters provide anchors or small barbs for improving position retention, which extend in radial directions outward from the ribs. Some filters may have barbs cut out from a central section of the filter. The barbs tend to gently hold the filter in place inside the vessel.
A vascular filter along the lines of the present invention may provide several advantages, including effectively capturing thrombus while allowing blood flow, resisting endothelialization of the filter, and distributing expansive pressures of the filter to a greater area of the vessel wall. In other words, there is less stress on the vessel wall, and the sleeve enables a physician to have a longer time before choosing whether to retrieve a retrievable filter.
A vascular filter may have an initial compressed shape, in which the filter may have essentially a tubular shape, and may be contained in a lumen or passage defined by a catheter.
After a distal tip of the catheter reaches a desired site for treatment, a wire mandrel or other deployment device may be used to push the filter out of the catheter. And when the filter is released from the catheter, it tends to resiliently expand from the initial compressed shape to an expanded shape. When a vascular filter is retrieved from a blood vessel, the entire filter is resiliently compressed to a relatively small diameter, for extraction through a catheter.
A filter according to the present invention has a flexible tubular covering on at least a portion of the filter. As a result, the filter exerts less expansive pressure on the vessel wall, and tends to resist incorporation into the vessel wall for a longer period of time.
The term “filter” will be used interchangeably, to refer to either (i) a combination device including a resilient scaffold structure with a sleeve covering, or (ii) only the scaffold component, or (iii) those portion(s) of the scaffold which operate to capture thrombus.
The term “tubular” is used in its broadest sense, to encompass any structure arranged a radial distance around a longitudinal axis. Accordingly, “tubular” includes any structure that (i) is cylindrical or not, such as for example an elliptical or polygonal cross-section, or any other regular or irregular cross-section; (ii) has a different or changing cross-section along its length; (iii) is arranged around a straight, curving, bent or discontinuous longitudinal axis; (iv) has an imperforate surface, or a periodic or other perforate, irregular or gapped surface or cross-section; (v) is spaced uniformly or irregularly, including being spaced varying radial distances from the longitudinal axis; (vi) has any desired combination of length or cross-sectional size.
A vascular filter may include a first and second filter section, arranged on either side of a body section. The body section and the filter sections thus enclose a space. Due to the elongated shape of the vascular filter, and the arranging of the first and second filter sections on either side of the body member, the present filter may have an enhanced filtering effect. In other words, two opportunities have been created for intercepting thrombus moving inside the blood vessel.
A central tubular section tends to resiliently exert slight outward pressure along a large section of contact area on the blood vessel wall. The sleeve distributes this outward pressure to a greater area. Accordingly, the filter tends to exert some small amount of pressure on the internal wall of the blood vessel, and tends to hold itself in place. The vascular filter will consequently tend not to shift position.
In addition, because of this elongated shape the vascular filter tends to center itself within the lumen, and not to rotate transversely or tilt over.
In an example, a vascular filter may be formed out of one single piece, which provides advantages including simplicity.
When viewed along the longitudinal axis of the filter, the filter sections may have the shape of a regular polygon, and thus may provide several smaller filtering “cells”. The purpose of these filtering cells is to intercept thrombus moving inside the blood vessel, and the smaller filtering cells tend to capture more thrombus. All the cells may be of the same size, to provide a uniform filtering effect.
The filter sections, as arranged according to an embodiment described above on either side of the tubular body section, may be identical in shape, thereby enhancing the simplicity of the vascular filter according to the present invention.
The sleeve of the present invention may be made of any suitable material, and may be affixed to the filter by friction alone, or with fasteners or adhesives of any suitable type. The sleeve may be foil, and/or may be elastic or inelastic. In addition, the sleeve may be biodegradable.
It is of course possible to build various vascular filters according to the present invention, by various techniques and of various materials to obtain the desired features. It should be noted that the present invention also relates to methods for manufacturing vascular filters, and for using vascular filters for medical treatment of a patient.
These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings. The invention will be explained in greater detail below with reference to the attached drawings of a number of examples of embodiments of the present invention.